1. Field of the Invention
The present invention relates to a radio-controlled timepiece.
2. Description of the Related Art
Conventionally, there has been an electronic timepiece (radio-controlled timepiece) which includes functions to receive a radio wave from a positioning satellite composing a global navigation satellite system such as GPS (Global Positioning System) of the United States to obtain time information, and to automatically correct the date and time being counted to display the correct date and time. In addition to GPS, as the global navigation satellite system, GLONASS of Russia and COMPASS of China are in use, and GALILEO of Europe and QZSS (Quasi-Zenith Satellite System) of Japan are being planned and tested. As for civilian use, there are many GPS which have already started operation.
The positioning satellite of the GPS (hereinafter referred to as GPS satellite) separately transmits timekeeping data output based on an atomic clock mounted inside the GPS satellite and correction data showing a difference from the UTC (Coordinated Universal Time) of the timekeeping data due to a leap second. Therefore, the present UTC date and time is obtained by correcting the timekeeping data with the value of the difference.
The value of the difference changes when a new leap second is inserted or deleted. At present, the leap second is executed irregularly by inserting a second after 23 hours 59 minutes 59 seconds or deleting 23 hours 59 minutes 59 seconds on June 30th and/or December 31st in the UTC as necessary. Therefore, the value of the difference needs to be suitably obtained and updated.
However, with the transmitting data of the GPS satellite, the date and time information can be obtained once every 6 seconds, however, the information regarding the leap second is transmitted only once every 12.5 minutes. Therefore, for radio-controlled timepieces, especially, portable timepieces with a small battery load capacity, receiving all pieces of data for 12.5 minutes or continuing reception until information regarding the leap second is obtained leads to a drastic increase in power consumption.
The following is disclosed as the conventional technique. The reception of the radio wave is paused after receiving the date/time information, and estimating the time until reaching the position where the information regarding the leap second is transmitted from the data position where the date/time information is obtained. The radio wave is received after the estimated time (for example, Japanese Patent Application Laid-Open Publication No. 2008-145287, Japanese Patent Application Laid-Open Publication No. 2009-250801). Moreover, it is also disclosed to receive such information regarding the leap second in June or December, and to reduce the receiving time from the GPS satellite in months where the leap second is not inserted.
However, according to the conventional technique, the radio wave needs to be received at least twice in order to obtain the data regarding the leap second from the positioning satellite. In order to reduce the load on the battery of radio-controlled timepieces, especially small or portable ones, there is a demand to suppress receiving time and receiving frequency from the positioning satellite as much as possible. On the other hand, in order to receive the necessary information in a small amount of receiving time, the operation of receiving needs to be performed at a suitable timing.